Cam thread-pulling device for the looper thread of a sewing machine

ABSTRACT

A thread tensioning device for the looper thread of a sewing machine which includes a cam driven by a rotating shaft, a mounting bracket, a plate member having an elongated opening through which the cam protrudes and means mounting the plate member on the mounting bracket whereby it can be rotated about an axis generally parallel to the axis of the rotating shaft to expose a selected amount of the cam profile.

United States Patent I191 Marforio 51 Sept. 9, 1975 CAM THREAD-PULLINGDEVICE FOR THE LOOPER THREAD ()F A SEWING MACHINE [75] Inventor: NerinoMarforio. Milan. Italy [73] Assignec: Virginie Rimoldi & C. S.p.A..Milan.

Italy 221 Filed: Mar. 20. I974 2| Appl.No.:452,7l9

[30] Foreign Application Priority Data Apr. l3, I973 Ituly r. 22983/73[52] US. Cl. 112/242 [5 1] Int. Cl. D058 49/00 [58] Field of Search112/242. 243, 254. 255. l [2/241 [56] References Cited UNITED STATESPATENTS l,(l64,l86 6/[9 3 Wuodwurd l 11/242 l ll8 322 ll/l9l4 Weisll2/242 X |.234.()94 7/!917 Drumheller. Ill/255 l 4()8 l85 2/1922Gutchell v r r .7 ll2/242 1866.427 l2/l958 lrmseher Ill/242 FOREIGNPATENTS OR APPLICATIONS 5fi9 7l4 6/1945 United Kingdom l l2/242 S [86753/l955 Italy .4 Ill/242 Primm v l;'.\'uminerGeorgc H. Krizmanich [57lABSTRACT A thread tensioning device for the looper thread of a sewingmachine which includes a cum driven by u rotuting shaft a mountingbracket. 11 plate member having an elongated opening through which thecum prutrudes and means mounting the plate member on the mountingbracket whereby it can be rotated about an axis generally parallel tothe axis of the rotating shaft to expose a selected amount of the camprofile.

2 Claims, 4 Drawing Figures PATENTEU BIBYS 3,903,821

sumlnrz CAM THREAILPULLING DEVICE FOR THE LOOPER THREAD OF A SEWINGMACHINE BACKGROUND OF THE INVENTION The present invention relates to alooper threadpulling device for sewing machines and particularly to sucha device. in which the thread is controlled by a cam opcratively drivenby a rotating shaft of the machine.

Known devices of this type are provided with a plate having a slit orelongated opening for receiving the cam. the plate which also carriesthread-guide means causing the thread to laterally cross the slit andthereby become subject to action of the cam. In known devices of thistype. the plate is fixed with screws to the frame of the machine. makingit possible to adjust its position in the direction of the axis of therotating shaft to center the cam perfectly in the slit in the plate.

The cam can be adjusted and fixed in any desired position during thetiming operation of the machine components. These thread pulling camshave the following functions:

a. to leave the looper thread slack when the looper is fully to theright of the axis along which the neetile is moving. so that thepreviously formed loop of the needle thread can be drawn upward:

b. to pull the looper thread when it enters the just formed needlethread loop. that is. when the looper begins its right-to-left travel;

c. to release temporarily the pull on the thread when the looper hasalready entered the loop and during the last part of the right-to-leftmovement thereof; and

d. to recover the looper thread when the latter begins its left-torightreturn stroke by taking up first the slack in the thread and thendrawing in further thread from a bobbin.

It is clear that in this last phase the cam must recover more or lessthread, according to the length of the leftto-right looper stroke. Thislength varies according to the number of needles and the distancebetween needles. More precisely. when a certain length of thread has tobe taken up for a single-needle sewing machine. the length of thread tobe taken up will be greater in a multi-needle machine, because thelength of the looper is greater.

In the known art. the takingup of a greater length of thread is effectedby adjusting sloted plate toward the shaft carrying the cam to increasethe amount of cam projecting over the plate top. increasing in thismanner the path of the thread between the two thread guides at the sidesof the cam. This type of adjustment is however limited because of thesize of the shaft and the cam support below the plate.

Another drawback is. that the vertical movement of the plate causes aslight delay in thread-taking up. so that the cam is no longer in propercondition to avoid a rather violent contact with the thread. Because ofthese drawbacks it is in most cases necessary to replace the cam with alarger one.

SUMMARY OF THE INVENTION It is the object of the present invention toobviate the above-mentioned trohlcs and to allow the use of a singlesize of cam independently of the number of needles and the distancebetween the said needles.

III

The present invention. comprises a device including a cam keyed to arotating shaft of the sewing machine. a plate overhanging and parallelto the rotating shaft with a slit or elongated opening allowing the camto penetrate thercthrough. thread guide means to adapt the thread to thecam contour. and means for regulating the section of the cam projectingthrough the slit of the plate.

DESCRIPTION OF THE DRAWINGS The present invention can best he understoodby ref ercnce to the following detailed description of a preferredembodiment thereof given as example. but not limited thereto. and byreference to the accompanying drawings. in which:

FIG. I illustrates a plan view of a front part ofa sew ing machine basecomprising the looper thread taking up device according to the presentinvention;

FIGS. 2. 3 and 4 show a perspective view of the device according to thepresent invention in three different working positions.

DESCRIPTION OF THE INVENTION The sewing machine chosen to illustrate thepresent invention is a machine of known type and it comprises. as shownin FIG. I, a base I housing longitudinally a rotating shaft 2 which maybe the main shaft of the machinev The base 1 contains also a looper 3mounted on a support 4 capable of moving along an almost elliptical pathformed by the combination of a movement substantially parallel to theaxis of main shaft 2 for the taking up and releasing of the needlethread loop. and a movement crosswise thereto. that is. substantiallyparallel to the direction of feed. The first movement suh stantiallyparallel to the axis of the main shaft 2 is obtained from the said mainshaft by means of transmissions of known type (not shown which transmitan alternating horizontal movement to a drawrod S. The drawrod 5 is asknown hinged to a pivot 6 which is an integral part ofthe support 4 of'thc looper 3. The second movement substantially parallel to thedirection of workpiece feed is also transmitted through the main shaft 2by known transmission means comprising an eccentric (not shown) whichengages a connecting rod 7. The free end of rod 7 is pivoted to an arm 8keyed to shaft 9 of the looper. onto which is clamped a sleeve I0. Thebase I also includes the lower transport components comprising amulti-claw feed dog I2 fixed to a support 13 hinged to the end 14between two parallel arms 15 that are fixed to the oscillating transportshaft 16.

Referring now to the drawing. the thread-pulling device for pulling thethread I8 of the looper 3 comprises a cam 19 formed of two equallyshaped discs 20, adjacent to and forming an integral part of a hub 21(FIGS. 2 and 3) the cam I9 is fixed with screws 22 to the main shaft 2.The thread pulling device 17, in addition to the cam I9, comprises arectangular support 23, rigidly fixed. in overhanding relationship tothe shaft 2, to a surface 24 on top of the dividing plate 25 of the baseI. The support 23, resting on the surface 24, abuts vertically againstthe dividing plate 25. The other side of the support 23 is provided witha hole for receiving a threaded pin 28 and a slot (FIG. 4) for receivingthe screw 30. Both the threaded pivot 28 and the screw 30 are screwed toa plate 31 on top of the main shaft 2. The axis of the screwed pin 28 isparallel to that of the shaft 2. and lies in essentially a commonvertical plane with the axis of shaft 2. The plate 3l comprises inaddition an elongated opening or slit 32 through which the cam 19 canpass. The plate 3| has, in addition a first thread guide 33 for leadingthe thread to disk thread tensioning device 34 of known type, and twofurther thread guides 35, 36, positioned respectively on opposite sidesof the slit 32 so that the thread will run substantially laterallyaccross the slit. Each of the thread guides 35, 36 is fixed to the plate31 by means of a screw 37 received in a slot 38 to permit adjustment ofthe said thread guide with respect to the cam axis. The plate 3! has, ina position located over the slit 32. two parallel arms 39, 40 soadjusted as to enter exactly between the two disks 20, the said armscarrying the thread 18 controlled by the thread guides 35, 36.

With particular reference to H65. 2. 3. 4, we shall now describe theoperation of the thread pulling device 17 during the looper threadtake-up phase. when the looper begins its left-to-right return stroke totake up thread slack. The cam I) initially contacts the thread [8between the two thread guides 35. 36 (FIG. 2), then begins to draw inthe looper thread by making it run in the track between the two parallelarms 39, 40 (H6. 3). Once the entire slack of the looper thread has beentaken up. the cam draws in further thread from a bobbin (not shown). Thethread taking-up action of the cam stops after partial rotation there.The interval of time for thread takingup obviously does not only dependon the contour of the cam, but also upon the relative position of thetwo thread guides 35, 36 and that of the two parallel arms 39, 40 withrespect to the cam. To increase the length of thread to be taken up fromthe looper as a function of the number of needles and as a function ofthe distance between the needles without having to change the moment inwhich thread taking-up begins and without having to replace the cam, itis sufficient to loosen the screw and rotate the plate 3] in downwarddirection around the threaded pin 28. Then the plate 31 is againsecurely fastened to the support 23 by tightening the screw 30, thusprecluding any rotation of the plate during operation of the sewingmachine. The downward rotation of the plate increases the time intervalthe cam remains in contact with the thread and therefore increases thelength of thread taken up, without however changing the time moment inwhich the said interval begins. This is essentially due to the fact thatthe rotation of the plate does not substantially change the position ofthe thread guides 35. 36, which are approximately in line with thethreaded pin 28. The rotation of the plate increases the cam sectionprojecting through the slit 32, thereby increasing the length of threadrunning through the track between the two parallel arms 39, 40.Obviously. modifications and variations can be made to this insertion,for example, the slot 29 could be made on the plate 31 instead of on thesupport 23; in addition, the various components can be replaced byother, technically equivalent ones without departing from the scope ofthe invention.

I claim:

I. A cam thread pulling device for the looper thread of a sewing machinecomprising a cam operatively driven by a rotating shaft, a supportbracket mounted on the sewing machine adjacent said cam, a plate memberincluding means defining an elongated opening therein through which saidcam can extend and including thread guiding means thereon to directthread in a direction substantially laterally across said elongatedopening. means securing said plate member to said support bracket foradjustable rotation about an axis sub stantially parallel to the axis ofthe rotating shaft to expose a selected amount of said cam beyond thesurface of said plate member and thereby provide for the take up ofdifferent lengths of thread, and means contacting said plate member andsaid support bracket to secure them together in a selected positionwhere no rotation of said plate member will occur during operation ofthe sewing machine.

2. A device according to claim I, wherein the said means providing theaxis of rotation for said plate member has its axis parallel to the axisof said rotating shaft and both axes lie in a common vertical plane.

1. A cam thread pulling device for the looper thread of a sewing machinecomprising a cam operatively driven by a rotating shaft, a supportbracket mounted on the sewing machine adjacent said cam, a plate memberincluding means defining an elongated opening therein through which saidcam can extend and including thread guiding means thereon to directthread in a direction substantially laterally across said elongatedopening, means securing said plate member to said support bracket foradjustable rotation about an axis substantially parallel to the axis ofthe rotating shaft to expose a selected amount of said cam beyond thesurface of said plate member and thereby provide for the take up ofdifferent lengths of thread, and means contacting said plate member andsaid support bracket to secure them together in a selected positionwhere no rotation of said plate member will occur during operation ofthe sewing machine.
 2. A device according to claim 1, wherein the saidmeans providing the axis of rotation for said plate member has its axisparallel to the axis of said rotating shaft and both axes lie in acommon vertical plane.